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Abstract:

An ink jet recording method includes an image formation step of forming
an image on a recording medium having an ink-receiving layer by ejecting
an ink from an ink jet recording head and a humidification step of
humidifying a gap between the recording head and the recording medium, in
which in the image formation step, at least a cyan ink containing a
specific dye and a magenta ink containing a specific dye are used.

Claims:

1. An ink jet recording method comprising: an image formation step of
forming an image on a recording medium having an ink-receiving layer by
ejecting an ink from an ink jet recording head; and a humidification step
of humidifying a gap between the recording head and the recording medium,
wherein in the image formation step, at least a cyan ink containing a dye
represented by general formula (I) and a magenta ink containing a dye
represented by general formula (II) are used: ##STR00010## wherein in
general formula (I), A, B, C, and D each independently represent a
six-membered ring having aromaticity, and at least one of A, B, C, and D
represents a pyridine ring or a pyrazine ring; M's each independently
represents a hydrogen atom, an alkali metal, ammonium, or organic
ammonium; E represents an alkylene group; X represents a
sulfo-substituted anilino group, a carboxy-substituted anilino group, or
a phosphono-substituted anilino group, and the substituted anilino group
may further contain one to four substituents of at least one type of
substituent selected from the group consisting of a sulfonic acid group,
a carboxy group, a phosphono group, a sulfamoyl group, a carbamoyl group,
a hydroxy group, an alkoxy group, an amino group, an alkylamino group, a
dialkylamino group, an arylamino group, a diarylamino group, an
acetylamino group, an ureido group, an alkyl group, a nitro group, a
cyano group, a halogen atom, an alkylsulfonyl group, and an alkylthio
group; Y represents a hydroxy group or an amino group; and a, b, and c
satisfy 0.ltoreq.a≦2.0, 0.ltoreq.b≦3.0, and
0.1.ltoreq.c≦3.0, provided that a+b+c=1.0 to 4.0 and general
formula (II) ##STR00011## wherein in general formula (II), R1,
R2, R3, and R4 each independently represent an alkyl
group; and M's each independently represent a hydrogen atom, an alkali
metal, ammonium, or organic ammonium.

2. The ink jet recording method according to claim 1, wherein the content
(% by mass) of the dye represented by general formula (II) in the magenta
ink is in the range of 1.5% by mass or more to 5.0% by mass or less with
respect to the total mass of the magenta ink.

3. The ink jet recording method according to claim 1, wherein each of
R2, R3, R4, and R5 in general formula (II) represents
an ethyl group.

4. The ink jet recording method according to claim 1, wherein the magenta
ink further contains a magenta dye having an inorganic-organic balance
value of 2.0 or more and a water-soluble organic compound having an
inorganic-organic balance value of 1.7 or more to 2.5 or less.

5. The ink jet recording method according to claim 4, wherein the magenta
dye having an inorganic-organic balance value of 2.0 or more in the
magenta dye is represented by general formula (III): ##STR00012##
wherein the dye represented by general formula (III) has an
inorganic-organic balance value of 2.0 or more; R5's each
independently represent a hydrogen atom, an alkyl group, a hydroxyalkyl
group, a cyclohexyl group, a monoalkylaminoalkyl group, or a
dialkylaminoalkyl group; M's each independently represent a hydrogen
atom, an alkali metal, ammonium, or organic ammonium; and R6
represents a linking group.

6. The ink jet recording method according to claim 4, wherein the magenta
ink contains 1,5-pentanediol serving as the water-soluble organic
compound having an inorganic-organic balance value of 1.7 or more to 2.5
or less.

7. The ink jet recording method according to claim 1, wherein the
humidification step is performed by supplying humidified air into the gap
between the recording head and the recording medium, and wherein the gap
between the recording head and the recording medium is filled with an
atmosphere having a temperature of 35.degree. C. or lower and an absolute
humidity of 0.013 kg/kgDA or higher.

8. An ink jet recording apparatus comprising: a plurality of ink storage
portions configured to store a plurality of inks; an image forming
portion configured to form an image on a recording medium having an
ink-receiving layer by ejecting an ink from an ink jet recording head;
and a unit configured to humidify a gap between the recording head and
the recording medium, wherein the plural inks stored in the plural ink
storage portions include a cyan ink containing a dye represented by
general formula (I) and a magenta ink containing a dye represented by
general formula (II): ##STR00013## wherein in general formula (I), A,
B, C, and D each independently represent an six-membered ring having
aromaticity, and at least one of A, B, C, and D represents a pyridine
ring or a pyrazine ring; M's each independently represents a hydrogen
atom, an alkali metal, ammonium, or organic ammonium; E represents an
alkylene group; X represents a sulfo-substituted anilino group, a
carboxy-substituted anilino group, or a phosphono-substituted anilino
group, and the substituted anilino group may further contain 1 to 4
substituents of at least one type of substituent selected from the group
consisting of a sulfonic acid group, a carboxy group, a phosphono group,
a sulfamoyl group, a carbamoyl group, a hydroxy group, an alkoxy group,
an amino group, an alkylamino group, a dialkylamino group, an arylamino
group, a diarylamino group, an acetylamino group, an ureido group, an
alkyl group, a nitro group, a cyano group, a halogen atom, an
alkylsulfonyl group, and an alkylthio group; Y represents a hydroxy group
or an amino group; and a, b, and c satisfy 0.ltoreq.a≦2.0,
0.ltoreq.b≦3.0, and 0.1.ltoreq.c≦3.0, provided that
a+b+c=1.0 to 4.0 ##STR00014## wherein in general formula (II), R1,
R2, R3, and R4 each independently represent an alkyl
group; and M's each independently represent a hydrogen atom, an alkali
metal, ammonium, or organic ammonium.

[0004] The output form of an image has rapidly shifted from a silver
halide process to an ink jet process because of an increase in the
quality of an image formed by an ink jet recording method. Under such
circumstances, an image is required to have higher fastness properties,
such as ozone resistance and bronzing resistance. For example,
International Publication No. WO2007/091631 discloses that excellent
ozone resistance is achieved by the use of an azaphthalocyanine dye, in
which outer aromatic rings of a phthalocyanine skeleton are
nitrogen-containing heteroaromatic rings.

[0005] To achieve higher quality of an image in an ink jet recording
method, there have been advances in the minimization of an ink droplet.
An increase in reliability has also been required. In recent years,
intermittent ejection stability has been one of particularly important
reliability issues. In the case of forming an image by ink jet recording
method, if a state is continued in which the recovery operation of a
recording head is not performed and in which an ink is not ejected from
an ejection orifice of the recording head for a certain period of time,
the evaporation of water and so forth in ink proceeds from the ejection
orifice of the recording head. Then when an attempt is made to eject the
next first droplet of the ink from the ejection orifice, the ink can be
unstably ejected or the ink cannot be ejected, thereby disturbing an
image. To improve the reliability, for example, Japanese Patent Laid-Open
No. 11-268256 discloses a recording method by which recording can be
performed even on a material with low affinity to ink and which
suppresses scattering of water from ink droplets and clogging of a
recording head by humidifying a gap between a recording head and a
recording medium.

SUMMARY OF THE INVENTION

[0006] The inventors have conducted intensive studies and have found that
the use of the azaphthalocyanine dye described in International
Publication No. WO2007/091631 improves the ozone resistance and the
bronzing resistance of an image formed on a recording medium having an
ink-receiving layer. However, it was also found that in the case where an
image is formed with ink containing the dye by an ink jet recording
method including a humidification step, another problem of a reduction in
the bronzing resistance of a secondary color image made of magenta and
cyan inks is caused.

[0007] Accordingly, aspects of the present invention provide an ink jet
recording method that suppresses a reduction in the bronzing resistance
of a secondary color image even if a gap between a recording head and a
recording medium is humidified to improve the intermittent ejection
stability of ink. Furthermore, aspects of the present invention provide
an ink jet recording apparatus that provides the foregoing beneficial
effects.

[0008] According to one aspect of the present invention, an ink jet
recording method includes an image formation step of forming an image on
a recording medium having an ink-receiving layer by ejecting an ink from
an ink jet recording head, and a humidification step of humidifying a gap
between the recording head and the recording medium, in which in the
image formation step, at least a cyan ink containing a dye represented by
general formula (I) and a magenta ink containing a dye represented by
general formula (II) are used:

##STR00001##

wherein in general formula (I), A, B, C, and D each independently
represent an six-membered ring having aromaticity, and at least one of A,
B, C, and D represents a pyridine ring or a pyrazine ring; M's each
independently represents a hydrogen atom, an alkali metal, ammonium, or
organic ammonium; E represents an alkylene group; X represents a
sulfo-substituted anilino group, a carboxy-substituted anilino group, or
a phosphono-substituted anilino group, and the substituted anilino group
may further contain one to four substituents of at least one type of
substituent selected from the group consisting of a sulfonic acid group,
a carboxy group, a phosphono group, a sulfamoyl group, a carbamoyl group,
a hydroxy group, an alkoxy group, an amino group, an alkylamino group, a
dialkylamino group, an arylamino group, a diarylamino group, an
acetylamino group, an ureido group, an alkyl group, a nitro group, a
cyano group, a halogen atom, an alkylsulfonyl group, and an alkylthio
group; Y represents a hydroxy group or an amino group; and a, b, and c
satisfy 0≦a≦2.0, 0≦b≦3.0, and
0.1≦c≦3.0, provided that a+b+c=1.0 to 4.0 and

##STR00002##

wherein in general formula (II), R1, R2, R3, and R4
each independently represent an alkyl group; and M's each independently
represent a hydrogen atom, an alkali metal, ammonium, or organic
ammonium.

[0009] Further features of the present invention will become apparent from
the following description of exemplary embodiments with reference to the
attached drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIGURE is a schematic diagram of the main portion of an ink jet
recording apparatus according to aspects of the present invention.

DESCRIPTION OF THE EMBODIMENTS

[0011] Embodiments of the present invention will be described below in
detail. Hereinafter, a dye represented by general formula (I) and a dye
represented by general formula (II) are also referred to as a dye of
general formula (I) and a dye of general formula (II), respectively. A
bronzing phenomenon is caused by aggregating and stacking a dye in an
ink-receiving layer of a recording medium. From the viewpoint of a
coloring material, the bronzing phenomenon is known to be significantly
caused in a phthalocyanine dye, which has excellent ozone resistance. The
dye of general formula (I), which is described below, used in aspects of
the present invention has improved ozone resistance by increasing
aggregability, so that the bronzing phenomenon is liable to occur. In the
case of humidifying a gap between a recording head and the recording
medium to improve intermittent ejection stability, the ink-receiving
layer of the recording medium absorbs water. This slows the penetration
of ink into the recording medium. So, the dye of general formula (I) is
liable to aggregate in the vicinity of a surface of the recording medium.
Thus, the bronzing phenomenon is more liable to occur. In the case where
a primary color image and a secondary color image are formed using the
same amount of a cyan ink applied, the total amount of the ink applied
per unit area of the secondary color image is larger than that of the
primary color image. This further slows the penetration of the ink into
the recording medium. So, the occurrence of the bronzing phenomenon is
particularly noticeable.

[0012] The inventors have conducted studies and have found that the
presence of the dye of general formula (II), which is described below, in
a magenta ink used together with the cyan ink containing the dye of
general formula (I) improves the bronzing resistance of the secondary
color image even when humidification is performed. The inventors
speculate that the reason for this is as follows: The dye of general
formula (II) has high fixability to the ink-receiving layer of the
recording medium. So, when an ink containing the dye of general formula
(II) is applied to the recording medium, the ink is readily fixed in the
vicinity of a surface of the ink-receiving layer of the recording medium
because of its high fixability. In the secondary color image formed using
the magenta ink and the cyan ink that contains the dye of general formula
(I), the dye of general formula (II) is probably arranged between
aggregates of the dye of general formula, thereby suppressing the
occurrence of the bronzing phenomenon. It is believed that in this case,
the dye of general formula (II) is arranged between the aggregates of the
dye of general formula (I) and thus does not inhibit the aggregation of
the dye of general formula (I), so that excellent ozone resistance of the
dye of general formula (I) is not impaired.

[0013] Ink Jet Recording Method

[0014] An aspect of the present invention is characterized by including an
image formation step of forming an image on a recording medium having an
ink-receiving layer using the plural inks and a humidification step of
humidifying a gap between a recording head and a recording medium.

[0015] Image Formation Step

[0016] In aspects of the present invention, the image formation step of
ejecting an ink from an ink jet recording head to form an image on a
recording medium having an ink-receiving layer is performed. In the image
formation step, at least a cyan ink containing a dye represented by
general formula (I) and a magenta ink containing a dye represented by
general formula (II) described below are used. The cyan ink and magenta
ink can be applied onto the recording medium so as to be overlapped in at
least one region of the recording medium, thereby forming an image
including a secondary color region. An exemplary method for ejecting an
ink includes applying thermal energy or mechanical energy to the ink. In
aspects of the present invention, a method for ejecting an ink by the
application of thermal energy can be employed.

[0017] Recording Medium

[0018] The recording medium used in aspects of the present invention may
have an ink-receiving layer and can have a glossy surface or a
semi-glossy surface. Specifically, the recording medium can have an
ink-receiving layer on at least one surface of a support, the
ink-receiving layer mainly containing a pigment composed of, for example,
silica, alumina, or its hydrate, and optionally containing an additive,
for example, a binder or a cationic polymer. In the recording medium, ink
is absorbed by pores of a porous structure formed of pigment particles to
form an image with high quality.

[0019] As the support, a support which is capable of being provided with
the ink-receiving layer and which has stiffness such that the support can
be conveyed by a conveying mechanism of an ink jet recording apparatus
can be used. An example of the support is paper containing pulp or a
filler. A recording medium may be used in which a resin layer composed
of, for example, polyolefin, is arranged on at least one surface of a
support and in which an ink-receiving layer is arranged on the resin
layer. Furthermore, a recording medium may be used in which ink-receiving
layers are arranged on both surfaces of a support.

[0020] The recording medium used in the ink jet recording method according
to aspects of the present invention may be cut into predetermined size in
advance. Alternatively, the recording medium may be a wound sheet in the
form of a roll, the wound sheet being to be cut into predetermined size
after the formation of an image.

[0023] A coloring material contained in the cyan ink used in aspects of
the present invention is a dye which has excellent ozone resistance and
which is represented by general formula (I):

##STR00003##

wherein in general formula (I), A, B, C, and D each independently
represent an six-membered ring having aromaticity, and at least one of A,
B, C, and D represents a pyridine ring or a pyrazine ring; M's each
independently represents a hydrogen atom, an alkali metal, ammonium, or
organic ammonium; E represents an alkylene group; X represents a
sulfo-substituted anilino group, a carboxy-substituted anilino group, or
a phosphono-substituted anilino group, and the substituted anilino group
may further contain one to four substituents of at least one type of
substituent selected from the group consisting of a sulfonic acid group,
a carboxy group, a phosphono group, a sulfamoyl group, a carbamoyl group,
a hydroxy group, an alkoxy group, an amino group, an alkylamino group, a
dialkylamino group, an arylamino group, a diarylamino group, an
acetylamino group, an ureido group, an alkyl group, a nitro group, a
cyano group, a halogen atom, an alkylsulfonyl group, and an alkylthio
group; Y represents a hydroxy group or an amino group; and a, b, and c
satisfy 0≦a≦2.0, 0≦b≦3.0, and
0.1≦c≦3.0, provided that a+b+c=1.0 to 4.0. In aspects of
the present invention, the content (% by mass) of the dye of general
formula (I) in the cyan ink may be in the range of 0.1% by mass or more
to 10.0% by mass or less, such as 0.5% by mass or more to 5.0% by mass or
less with respect to the total mass of the ink. A content of less than
0.1% by mass can lead to an image having insufficient ozone resistance. A
content of more than 10.0% by mass can lead to insufficient ejection
stability of the ink.

[0024] In general formula (I), A, B, C, and D each independently represent
a six-membered ring having aromaticity, and at least one of A, B, C, and
D represents a pyridine ring or a pyrazine ring. Examples of the
six-membered ring having aromaticity include a benzene ring, a pyridine
ring, and a pyrazine ring. Among these rings, a pyridine ring can be
used. In aspects of the present invention, a dye can be used in which one
to three of A, B, C, and D is pyridine rings or pyrazine rings and in
which the remainder is a benzene ring.

[0025] In general formula (I), E represents an alkylene group. The number
of carbon atoms in the alkylene group is may be in the range of 2 to 12
and such as 2 to 6. Specific examples of the alkylene group include an
ethylene group, a propylene group, a butylene group, a pentylene group, a
hexylene group, a cyclopropylenediyl group, a 1,2- or
1,3-cyclopentylenediyl group, and a 1,2-, 1,3-, or 1,4-cyclohexylene
group. Among these groups, an ethylene group, a propylene group, and a
butylene group can be used.

[0026] In general formula (I), X represents a sulfo-substituted anilino
group, a carboxy-substituted anilino group, or a phosphono-substituted
anilino group. The substituted anilino group may further contain zero to
four substituents and even zero to two of at least one type of
substituent selected from the group consisting of a sulfonic acid group,
a carboxy group, a phosphono group, a sulfamoyl group, a carbamoyl group,
a hydroxy group, an alkoxy group, an amino group, an alkylamino group, a
dialkylamino group, an arylamino group, a diarylamino group, an
acetylamino group, an ureido group, an alkyl group, a nitro group, a
cyano group, a halogen atom, an alkylsulfonyl group, and an alkylthio
group. Specific examples of X include a 2,5-disulfoanilino group, a
2-sulfoanilino group, a 3-sulfoanilino group, a 4-sulfoanilino group, a
2-carboxyanilino group, a 4-ethoxy-2-sulfoanilino group, a
2-methyl-5-sulfoanilino group, a 2-methoxy-4-nitro-5-sulfoanilino group,
a 2-chloro-5-sulfoanilino group, a 3-carboxy-4-hydroxyanilino group, a
3-carboxy-4-hydroxy-5-sulfoanilino group, a
2-hydroxy-5-nitro-3-sulfoanilino group, 4-acetylamino-2-sulfoanilino
group, a 4-anilino-3-sulfoanilino group, a 3,5-dicarboxyanilino group, a
2-carboxy-4-sulfamoylanilino group, a 2,5-dichloro-4-sulfoanilino group,
and a 3-phosphonoanilino group. In general formula (I), Y represents a
hydroxy group or an amino group.

[0027] In general formula (I), for example, a sulfonic acid group, a
carboxy group, and a phosphono group may be in the form of a salt.
Examples of a counter ion that can form a salt include ions of alkali
metals, ammonium ions, and organic ammonium ions. Examples of the alkali
metal include lithium, sodium, and potassium. Examples of the organic
ammonium include alkylamines having 1 to 3 carbon atoms, such as
methylamine and ethylamine; and onium salts of mono-, di-, or
tri-alkanolamine having 1 to 4 carbon atoms, such as monoethanolamine,
diethanolamine, triethanolamine, monoisopropanolamine,
diisopropanolamine, and triisopropanolamine. An alkali-earth metal, for
example, calcium or magnesium, may be used as the counter ion.

[0028] Specific examples of the dye of general formula (I) include
exemplified compounds C1 to C24 shown in Table 1. Table 1 shows groups of
A, B, C, D, E, X, and Y in general formula (I). The dye according to
aspects of the present invention is not limited to the exemplified
compounds described below as long as it has a structure included in the
structure of general formula (I) and it is included in the definition of
general formula (I). Because at least one of A, B, C, and D in general
formula (I) is a pyridine ring or a pyrazine ring, regioisomers with
respect to the position of the nitrogen atom are present. So, in the case
of synthesizing a compound, a mixture of these regioisomers is obtained.
It is difficult to isolate these isomers. Furthermore, it is difficult to
identify these isomers by analysis. Thus, the dye of general formula (I)
is usually used as a mixture. However, even when the dye contains these
isomers, the advantageous effects of aspects of the present invention are
obtained without change. So, in this specification, these isomers are not
distinguished. With respect to A, B, C, and D in general formula (I)
according to aspects of the present invention, the number of pyridine
rings may be in the range of 1 to 3, such as 1 to 2. Specifically, among
the exemplified compounds, exemplified compounds C1 to C3, C10 to C12,
and C21 to C23 can be used.

[0030] A coloring material contained in the magenta ink used in aspects of
the present invention is a dye which has relatively high hydrophobicity
and high fixability to the ink-receiving layer of the recording medium
and which is represented by general formula (II):

##STR00004##

wherein in general formula (II), R1, R2, R3, and R4
each independently represent an alkyl group; and M's each independently
represent a hydrogen atom, an alkali metal, ammonium, or organic
ammonium. In aspects of the present invention, the content (% by mass) of
the dye of general formula (II) in the magenta ink can be in the range of
1.5% by mass or more to 5.0% by mass or less with respect to the total
mass of the ink. A content of less than 1.5% by mass or a content of more
than 5.0% by mass can lead to a secondary color image having insufficient
bronzing resistance. In particular, a content of more than 5.0% by mass
results in an excessive amount of the dye of general formula (II) fixed
in the vicinity of a surface of the ink-receiving layer of the recording
medium. This excessively inhibits the penetration of the cyan ink into
the recording medium. As a result, the dye of general formula (I) can be
readily aggregated in the vicinity of the surface of the ink-receiving
layer of the recording medium, thus resulting in insufficient bronzing
resistance.

[0031] The alkyl group in general formula (II) can have 1 to 3 carbon
atoms from the viewpoint of achieving good solubility in an aqueous
medium contained in the ink. Specific examples thereof include a methyl
group, an ethyl group, a primary propyl group, and a secondary propyl
group. If the number of carbon atoms in the alkyl group is 4 or more, the
coloring material can have excessively high hydrophobicity and thus can
be less likely to be dissolved in the aqueous medium contained in the
ink.

[0032] In general formula (II), M's each independently represent a
hydrogen atom, an alkali metal, ammonium, or organic ammonium. Examples
of the alkali metal include lithium, sodium, and potassium. Examples of
the organic ammonium include acetamide, benzamide, methylamino,
butylamino, diethylamino, triethylamine, and phenylamino.

[0033] Examples of the dye of general formula (II) can include exemplified
compounds M1 and M2 described below. Note that the following exemplified
compounds are described in the form of a free acid. The dye according to
aspects of the present invention is not limited to the exemplified
compounds described below as long as it has a structure included in the
structure of general formula (II) and it is included in the definition of
general formula (II). In aspects of the present invention, among these
exemplified compounds described above, exemplified compound M2, in which
each of R1, R2, R3, and R4 in general formula (II)
represents an ethyl group, can be used.

##STR00005##

[0034] Preferred Embodiments of Magenta Ink: Magenta Dye Having IOB Value
of 2.0 or More and Water-Soluble Organic Compound Having IOB Value of 1.7
or More to 2.5 or Less

[0035] As described above, intermittent ejection stability is one of
particularly important reliability issues. In addition, it is also
important to overcome another problem of an increase in concentration at
a beginning portion. The increase in concentration at a beginning portion
is defined as a phenomenon caused by a relative increase in the
concentration of a dye in an ink present in the vicinity of an ejection
orifice of a nozzle due to the evaporation of water in ink present in the
nozzle of a recording head. When an image is formed in this state, the
image density of a beginning portion (portion where the formation of the
image begins) of the image is higher than that of another portion. This
is a problem for the formation of a high-quality image.

[0036] As described above, the increase in concentration at a beginning
portion is caused by the evaporation of water in the ink. Like
improvement in intermittent ejection stability due to humidification, it
was predicted that the increase in concentration at a beginning portion
could be suppressed by humidification. Contrary to this prediction,
however, the results of studies by the inventors demonstrated that
although the intermittent ejection stability by humidification was
improved, the increase in concentration at a beginning portion was not
improved. The reason the difference is made is speculated as follows: The
direct cause of a reduction in intermittent ejection stability is a local
increase in the viscosity of the ink due to the evaporation of water. The
increase in concentration at a beginning portion is caused by a local
increase in the concentration of the dye in the ink due to the
evaporation of water. So, they are attributed to different phenomena. The
humidification within a practical range such that condensation is not
formed on the recording head suppresses the evaporation of water to the
extent that the viscosity of the ink is not increased. However, the
humidification does not have the effect of suppressing the increase in
the concentration of the dye. As described above, there is a limitation
in the suppression of the increase in concentration at a beginning
portion by, for example, humidification.

[0037] In particular, for the magenta ink in which only the dye of general
formula (II) is contained as a coloring material, the increase in
concentration at a beginning portion occurred noticeably. The reason for
this is speculated as follows: The dye of general formula (II) has
relatively high hydrophobicity among dyes to be contained in ink for use
in ink jet printing and thus has a high solubility in various
water-soluble organic solvents commonly used for ink. The dye has a high
solubility in the water-soluble organic solvent even when the content of
water in the ink is relatively reduced by the evaporation of water from
the ejection orifice. So, the concentration of the dye is relatively
increased by a reduction in the amount of water, thereby increasing the
concentration of the dye in the first droplet.

[0038] In the case of a magenta ink in which only a dye having relatively
high hydrophilicity instead of the dye of general formula (II) is
contained as a coloring material, the dye has a low solubility in various
water-soluble organic solvent commonly used in ink. So, the dye is no
longer dissolved in a portion of the ink where the content of water is
relatively reduced due to the evaporation of water from the ejection
orifice. The dye moves toward the backside of the nozzle (the direction
opposite to the ejection orifice). This suppresses the increase in the
concentration of the dye in the first ink droplet ejected. In this case,
however, the concentration of the dye in the first ink droplet ejected is
reduced. In addition, although the concentration of the dye in the second
ink droplet ejected is increased to a level, the level is lower than the
concentration in the first droplet of the ink containing the dye of
general formula (II). As a result, the increase in concentration at a
beginning portion of an image is still caused.

[0039] So, the inventors have conducted studies and have found that the
use of an ink containing a dye having relatively high hydrophilicity and
a water-soluble organic compound having relatively high hydrophobicity in
addition to the dye, having relatively high hydrophobicity, of general
formula (II) suppresses the increase in concentration at a beginning
portion of an image. The reason for this is presumably that in the case
of the ink containing these components, the concentrations of the dyes in
the first ink droplet and the second ink droplet are both increased, so
that the difference in image density at a beginning portion of a formed
image is unremarkable.

[0040] The inventors have paid attention to the ratio of an inorganic
value and an organic value, i.e., an inorganic-organic balance (IOB,
inorganic value/organic value), based on the theory of an organic
conceptual diagram, the IOB value serving as an index of the properties
of an organic compound. The organic conceptual diagram is a diagram in
which properties of an organic compound are divided into the organic
value that indicates covalency and the inorganic value that indicates
ionicity and in which they are plotted on rectangular coordinates with
the organic axis (horizontal axis) and the inorganic axis (vertical
axis). The organic value is substantially equal to the product of the
number of carbon atoms of a compound and 20. The inorganic value is
defined as the sum of inorganic values intrinsic to groups.

[0041] In reference 1 (Yosio Koda. "Yuki Gainen Zu -Kiso to Oyo-"
("Organic Conceptual Diagram, Foundation and Application"); Sankyo
Shuppan, 1984), the inorganic values of about 80 groups are determined to
date; for example, the inorganic value of a hydroxy group is defined as
100. Reference 2 (Ryohei Oda. "Teijin Taimusu" ("Teijin Times"), 22(9),
10-4 (1952)) describes the following: The organic nature in the organic
conceptual diagram corresponds to the lipophilicity (i.e.,
hydrophobicity) of a surfactant. So, the ratio of the inorganic nature to
the organic nature calculated on the basis of the chemical structure of a
surfactant has the same meaning as the hydrophile-lipophile balance (HLB)
of the surfactant. Conversely, the IOB value can be regarded as an index
that indicates the hydrophobicity of an organic compound.

[0042] As described above, the use of the ink containing a dye having
relatively high hydrophilicity and a water-soluble organic compound
having relatively high hydrophobicity in addition to the dye, having
relatively high hydrophobicity, of general formula (II) suppresses the
increase in concentration at a beginning portion of an image. The degree
of hydrophobicity of the water-soluble organic compound can be determined
by the IOB value. The inventors have paid attention to the dye having
relatively high hydrophilicity and the water-soluble organic compound
having relatively high hydrophobicity and have conducted studies of
ranges of their IOB values. Thus, the inventors have found that an ink
containing a magenta dye having an IOB value of 2.0 or more and a
water-soluble organic compound having an IOB value of 1.7 or more to 2.5
or less in addition to the dye of general formula (II) is appropriately
used.

[0043] Note that the relationship between the dye and the water-soluble
organic compound in terms of the solubility of the dye in the
water-soluble organic compound is not yet clear. However, results from
studies by the inventors at least demonstrate that a dye having an IOB
value of 1.5 to 1.8 is well soluble in a water-soluble organic compound
having an IOB value of 1.4 to 5.0 and that a dye having an IOB value of
2.0 or more is less soluble in a water-soluble organic compound having an
IOB value of 2.5 or less. Magenta Dye Having IOB Value of 2.0 or More

[0044] The magenta ink can contain a magenta dye having an IOB value of
2.0 or more. The upper limit of the IOB value can be 3.0 or less. The
content (% by mass) of the magenta dye having an IOB value of 2.0 or more
in the magenta ink can be in the range of 1.0% by mass or more to 5.0% by
mass or less with respect to the total mass of the ink. A content of less
than 1.0% can fail to sufficiently suppress the increase in the
concentration at a beginning portion. At a content of more than 5.0% by
mass, after a state is continued in which the ink is not ejected from an
ejection orifice of a recording head for a certain period of time, the
concentration of the dye in the second ink droplet ejected is higher than
that in the first ink droplet, thereby failing to sufficiently suppress
the increase in the concentration at a beginning portion, in some cases.

[0045] Examples of the magenta dye having an IOB value of 2.0 or more can
include dyes represented by general formulae (III), (IV), and (V). In
aspects of the present invention, among these magenta dyes each having an
IOB value of 2.0 or more, the dye represented by general formula (III)
described below can be used because the increase in concentration at a
beginning portion is markedly suppressed:

##STR00006##

wherein the dye represented by general formula (III) has an IOB value of
2.0 or more; R5's each independently represent a hydrogen atom, an
alkyl group, a hydroxyalkyl group, a cyclohexyl group, a
monoalkylaminoalkyl group, or a dialkylaminoalkyl group; M's each
independently represent a hydrogen atom, an alkali metal, ammonium, or
organic ammonium; and R6 represents a linking group.

[0046] In general formula (III), in the case where each R5 represents
a group having a carbon atom, the number of carbon atoms may be in the
range of 1 to 8, such as 1 to 4. In general formula (III), R6
represents a linking group having a structure, for example,
*--NH--(CH2)n--NH--* (n represents 2 to 8, such as 2 to 6, and
even 2; and *'s represent linking sites to be linked with two different
triazine rings). In general formula (III), M's each independently
represent an alkali metal, ammonium, or organic ammonium. Examples of the
alkali metal include lithium, sodium, and potassium. Examples of the
organic ammonium include acetamide, benzamide, methylamino, butylamino,
diethylamino, and phenylamino.

##STR00007##

wherein a dye represented by general formula (IV) has an IOB value of 2.0
or more; R7 represents a hydrogen atom or an alkyl group; d
represents an integer of 1 to 3; and M's each independently represent a
hydrogen atom, an alkali metal, ammonium, or organic ammonium.

[0047] In general formula (IV), R7 represents a hydrogen atom or an
alkyl group. The number of carbon atoms in the alkyl group may be in the
range of 1 to 8, such as preferably 1 to 4. In general formula (IV), M's
each independently represent a hydrogen atom, an alkali metal, ammonium,
or organic ammonium. Examples of the alkali metal include lithium,
sodium, and potassium. Examples of the organic ammonium include
acetamide, benzamide, methylamino, butylamino, diethylamino, and
phenylamino.

##STR00008##

wherein a dye represented by general formula (V) has an IOB value of 2.0
or more; R8, R9, and R10 each independently represent an
alkyl group, an alkoxy group, a halogen atom, a hydrogen atom, a hydroxy
group, a carbamoyl group, a sulfamoyl group, an amino group, a nitro
group, a sulfonic ester group, a carboxy group, or a carboxylate group;
R11, R12, and R13 each independently represent a hydrogen
atom, an alkyl group, an alkenyl group, an aryl group, an aralkyl group,
an aromatic group, or a heterocyclic group; e represents an integer of 0
to 3; and M's each independently represent a hydrogen atom, an alkali
metal, ammonium, or organic ammonium.

[0048] In general formula (V), in the case where each of R8, R9,
R10, R11, R12, and R13 represents a group having a
carbon atom, the number of carbon atoms may be in the range of 1 to 8,
such as 1 to 4. In general formula (V), M's each independently represent
a hydrogen atom, an alkali metal, ammonium, or organic ammonium. Examples
of the alkali metal include lithium, sodium, and potassium. Examples of
the organic ammonium include acetamide, benzamide, methylamino,
butylamino, diethylamino, and phenylamino.

[0049] A specific example of the dye represented by general formula (III)
is exemplified compound M3 described below. A specific example of the dye
represented by general formula (IV) is exemplified compound M4 described
below. A specific example of the dye represented by general formula (V)
is exemplified compound M5 described below. Note that the following
exemplified compounds are described in the form of a free acid. These
dyes according to aspects of the present invention are not limited to the
exemplified compounds described below as long as they have structures
included in the structures of general formulae (III), (IV), and (V) and
they are included in the definition thereof.

##STR00009##

[0050] Water-Soluble Organic Compound Having IOB Value of 1.7 or More to
2.5 or Less

[0051] The magenta ink can contain the magenta dye having an IOB value of
2.0 or more in combination with the water-soluble organic compound having
an IOB value of 1.7 or more to 2.5 or less, as described above. An IOB
value of the water-soluble organic compound of less than 1.7 can lead to
the precipitation of the high-hydrophilic dye having an IOB value of 2.0
or more at the tip of a nozzle because of excessively high hydrophobicity
of the water-soluble organic compound, thereby failing to sufficiently
providing the effect of suppressing the increase in concentration at a
beginning portion using the dye. An IOB value of more than 2.5 can lead
to insufficient suppression of the increase in the concentration at a
beginning portion. In this aspect of the present invention, the foregoing
effect is provided as long as the magenta ink contains the water-soluble
organic compound having an IOB value of 1.7 or more to 2.5 or less. Thus,
the magenta ink may further contain a water-soluble organic compound
having an IOB value of less than 1.7 or more than 2.5.

[0052] Examples of the water-soluble organic compound which has an IOB
value of 1.7 or more to 2.5 or less and which can be contained in the
magenta ink used in aspects of the present invention are described below,
and each of the numbers in parentheses represents the IOB value. Examples
thereof include 1,4-butanediol (2.5), 1,5-pentanediol (2.0),
2-pyrrolidone (1.8), 3-methyl-1,5-pentanediol (1.8), 1,2-hexanediol
(1.7), and 1,6-hexanediol (1.7). They may be contained in the ink
separately or in combination. In aspects of the present invention, the
water-soluble organic compound is not limited to the foregoing compounds.
Any water-soluble organic compound may be used without limitation as long
as it has an IOB value within the range described above. In aspects of
the present invention, among these water-soluble organic compounds,
1,5-pentanediol can be used.

[0053] In aspects of the present invention, letting the content of the
magenta dye having an IOB value of 2.0 or more in the magenta ink be A (%
by mass), and letting the content of the water-soluble organic compound
having an IOB value of 1.7 or more to 2.5 or less be B (% by mass), the
following relationship can be satisfied. The mass ratio (B/A) of the
content B (% by mass) of the water-soluble organic compound having an IOB
value of 1.7 or more to 2.5 or less to the content A (% by mass) of the
dye represented by general formula (II), i.e., B/A, may be in the range
of 0.5 times or more to 15.0 times or less, such as 1.0 time or more to
10.0 times or less with respect to the total mass of the ink. A mass
ratio of less than 0.5 times can lead to the insufficient effect of
suppressing the increase in the concentration at a beginning portion. A
mass ratio of more than 15.0 times can lead to insufficient intermittent
ejection stability because of the excessively high viscosity of the ink.

[0054] In aspects of the present invention, our attention is focused on
the affinity between the dye and the water-soluble organic compound. So,
the term "the water-soluble organic compound" having an IOB value, which
is determined by calculation, does not include coloring materials, such
as dyes and pigments, and additives as described below.

[0055] Aqueous Medium

[0056] Each ink may contain an aqueous medium, which is a mixed solvent of
water and a water-soluble organic solvent. The magenta ink may further
contain the foregoing water-soluble organic compound having an IOB value
within the specific range. Deionized water and ion-exchanged water can be
used as water. The content (% by mass) of water in the ink can be in the
range of 50.0% by mass or more to 95.0% by mass or less with respect to
the total mass of the ink. Examples of the water-soluble organic solvent
include monohydric and polyhydric alcohols, glycols, glycol ethers, and
nitrogen-containing compounds, which can be used for ink for use in ink
jet printing. These compounds may be contained in the ink separately or
in combination. The content (% by mass) of the water-soluble organic
solvent in the ink can be in the range of 2.0% by mass or more to 50.0%
or less by mass with respect to the total mass of the ink. In this case,
the content of the water-soluble organic solvent includes the content of
the water-soluble organic compound having an IOB value within the
specific range.

[0057] Additional Additive

[0058] Each ink used in aspects of the present invention may contain a
solid water-soluble organic compound at room temperature, for example,
urea, its derivative, or polyhydric alcohol, e.g., trimethylolpropane or
trimethylolethane. Furthermore, the ink may optionally contain various
additives in addition to the components described above. Examples of the
additives include surfactants, pH adjusting agents, rust-preventive
agents, preservatives, fungicides, antioxidants, anti-reducing agents,
evaporation accelerators, chelating agents, and water-soluble polymers.

[0059] Additional Ink

[0060] In aspects of the present invention, as the ink used in the image
formation step, at least the cyan ink and the magenta ink described above
are used. Furthermore, an additional type of ink may be used. Examples of
the additional type of ink include yellow, black, red, green, and blue
inks. Moreover, inks having the same hues but different concentrations
from these inks and clear inks, which do not contain a coloring material,
may be used.

[0061] Humidification Step

[0062] An aspect of the present invention includes the foregoing image
formation step and a humidification step of humidifying a gap between a
recording head and a recording medium. The humidification step may be
performed to the extent that the ink-receiving layer of the recording
medium sufficiently absorbs water. An example of a humidification method
is a method in which humidified air is fed into the gap between the
recording head and the recording medium. In aspects of the present
invention, the humidification step is performed by supplying humidified
air into the gap between the recording head and the recording medium. The
humidification step can be performed in such a manner that the gap
between the recording head and the recording medium is filled with an
atmosphere having a temperature of 35° C. or lower and an absolute
humidity of 0.013 kg/kgDA or higher. Here, the term "absolute humidity"
used aspects of the present invention indicates an absolute humidity on a
weight basis, i.e., the weight (kg) of water vapor contained in
humidified air with respect to the weight (kg) of dry air as expressed by
the unit kg/kgDA. The lower limit of the temperature can be 15° C.
or higher. As a precondition, the relative humidity can be lower than
100%. With respect to the humidification conditions, the atmosphere can
have a temperature of 15° C. or higher to 35° C. or lower
and an absolute humidity of 0.015 kg/kgDA or higher and even 0.017
kg/kgDA or higher. In this case, the effect of improving the intermittent
ejection stability by humidification is high, and the relative humidity
is lower than 100% in this temperature range. Thus, no condensation
occurs on the recording head, providing excellent ejection stability.

[0063] Aspects of the present invention, in addition to the humidification
step described above, a prehumidification step of humidifying a recording
medium can be performed before the image formation step. In this step,
the recording medium is humidified before the recording medium is
conveyed to an image forming portion including the recording head. The
intermittent ejection stability is more effectively improved by
performing this prehumidification step. The reason for this is as
follows: The prehumidification step allows the recording medium to
sufficiently absorb water before the recording medium is conveyed to the
image forming portion. This makes it possible to effectively humidify the
gap between the recording head and the recording medium. In aspects of
the present invention, the prehumidification step is performed by
supplying humidified air before the recording medium is conveyed to the
image forming portion including the recording head. The prehumidification
step can be performed in an atmosphere having a temperature of 35°
C. or lower and an absolute humidity of 0.013 kg/kgDA or higher.

[0064] Ink Jet Recording Apparatus

[0065] An ink jet recording apparatus according to aspects of the present
invention includes a plurality of ink storage portions configured to
store a plurality of inks, an image forming portion configured to form an
image on a recording medium having an ink-receiving layer by ejecting an
ink from an ink jet recording head, and a unit configured to humidify a
gap between the recording head and the recording medium, in which the
plural inks stored in the plural ink storage portions include the cyan
ink and the magenta ink described above.

[0066] The structure of the ink jet recording apparatus according to
aspects of the present invention will be described below. FIGURE is a
schematic diagram of an exemplary image forming portion 1 of the ink jet
recording apparatus used in the ink jet recording method according to
aspects of the present invention. The illustration of the entire
structure of the recording apparatus is omitted. A paper feeding unit,
the image forming portion 1, a cutting unit, a drying unit, the ink
storage portions, a control unit, and a paper ejecting section are
arranged from the upstream side to the downstream side of the conveying
direction of the recording medium. The paper feeding unit rotatably holds
a recording medium 2 wound in the form of a roll. The image forming
portion 1 includes a plurality of recording heads la corresponding to
inks of different colors. Here, four recording heads corresponding to the
four inks are arranged. However, the number of inks is not limited to
four. Each of the inks is fed from the ink storage portions to a
corresponding one of the recording heads la through ink tubes. Each of
the plural recording heads la is a line-type recording head provided with
an ink jet nozzle array that covers the maximum width of the recording
medium to be used.

[0067] Unlike a serial-type recording head in which a recording medium is
conveyed in a sub-scanning direction with the recording head scanned
reciprocally in a main scanning direction to form an image, in the case
of the line-type recording head, the recording head is not scanned
reciprocally. So, the line-type recording head has a significant
advantage in terms of recording rate over the serial-type recording head.
However, from the viewpoint of solving the foregoing problem of the
increase in the concentration at a beginning portion, the line-type
recording head is disadvantageous compared with the serial-type recording
head. The reason for this is as follows: For the serial-type recording
head, because reciprocal scanning is performed, what is called
preliminary ejection of ink having a relatively increased dye
concentration is performed at a position different from a position
corresponding to the recording medium even during a recording operation,
thereby suppressing the increase in the concentration at a beginning
portion. However, the line-type recording head is always located at a
position corresponding to a recording region. So, it is difficult to
perform the preliminary ejection as described above. Even when the
line-type recording head is used, the use of the magenta ink containing
the dye and the water-soluble organic compound described above
effectively suppresses the increase in the concentration at a beginning
portion.

[0068] In the image forming portion 1, a recording medium conveying path
is arranged transversely and faces the recording heads 1a. A conveying
mechanism configured to convey the recording medium is arranged along the
recording medium conveying path. The plural recording heads la and the
conveying mechanism are arranged in a substantially enclosed space in a
housing 1b. A second humidifying unit 1d configured to humidify the gap
between the recording heads la and the recording medium is arranged in
the image forming portion 1 and supplies humidified air into the gap
between the recording heads la and the recording medium (i.e., paper-head
distance). The humidified air may be fed not only into the gap between
the recording heads la and the recording medium but also into the whole
of the substantially enclosed space in the housing 1b to fill the whole
of the space with an atmosphere that satisfies predetermined temperature
and humidity conditions. Furthermore, a first humidifying unit 1c
configured to preliminarily humidify the recording medium before the
recording medium is conveyed to the image forming portion including the
recording heads may be arranged on the upstream side of the recording
heads 1a in the conveying direction.

[0069] The cutting unit is configured to cut the recording medium, on
which an image has been formed at the image forming portion 1, into a
predetermined size. The cutter unit includes a cutting mechanism. The
drying unit is configured to dry the cut recording medium in a short
time. The drying unit includes a hot-blast device provided with a heater
configured to heat a gas and a fan configured to generate the flow of the
heated gas, and a plurality of conveying rollers arranged along the
recording medium conveying path. The paper ejecting section is configured
to accommodate the cut recording medium ejected from the drying unit. A
plurality of pieces of the recording medium are stacked therein. The
control unit serves as a controller responsible for controlling and
driving the entire recording apparatus.

[0070] Note that the predetermined temperature and humidity conditions
described above can be achieved without performing the humidification
step, depending on an environment where the ink jet recording apparatus
is placed. However, the temperature and humidity in the outside
environment are always changed. So, the predetermined temperature and
humidity conditions are not always satisfied. Accordingly, the
achievement of the temperature and humidity conditions, which are set in
the aspects of the present invention, by performing the humidification
step remains effective in providing the advantages of aspects of the
present invention.

EXAMPLES

[0071] While the present invention will be described in more detail below
by way of Examples and Comparative Examples, the present invention is not
limited to the following Examples.

[0072] Preparation of Ink

[0073] Components (unit: % by mass) shown in Tables 2 to 4 described below
were mixed and sufficiently stirred to dissolve the components. The
resulting solution was filtered under pressure with a microfilter
(manufactured by Fujifilm Corporation) having a pore size of 0.2 μm to
prepare cyan and magenta inks. Acetylenol E100 is a nonionic surfactant
manufactured by Kawaken Fine Chemicals Co., Ltd. Note that for the
components of the magenta inks shown in Tables 3 and 4, each of the
numbers in parentheses represents the IOB value.

[0074] As exemplified compound C1, a compound synthesized on the basis of
Examples described in International Publication No. WO2007/091631 was
used. Note that dyes of general formula (I) are all mixtures. The
mixtures of isomers and so forth are referred to as "dyes". That is, the
dyes include, for example, regioisomers of compounds, regioisomers in
terms of the position of the nitrogen atom in a pyridine ring, isomers
having different ratios of benzo rings to nitrogen-containing
heteroaromatic rings represented by A, B, C and D in general formula (I),
and α/β regioisomers of a substituted or unsubstituted
sulfamoyl group in a benzo ring. As a comparative compound, compound 154
synthesized on the basis of Examples described in Japanese Patent
Laid-Open No. 2003-231834 was used.

[0075] As exemplified compounds M1 and M2, compounds synthesized on the
basis of Examples described in Japanese Patent Laid-Open No. 2006-143989
were used. As exemplified compound M5, a compound synthesized on the
basis of Examples described in Japanese Patent Laid-Open No. 8-073791 was
used. As exemplified compound M3, a compound synthesized on the basis of
Examples described in International Publication No. WO2008/066062 was
used. As exemplified compound M4, a compound synthesized on the basis of
Examples described in International Publication No. WO2004/104108 was
used. As reference compound (magenta dye having an IOB value of 1.2), a
compound of formula (1) synthesized on the basis of Examples described in
Japanese Patent Laid-Open No. 2000-169776 was used.

[0078] The rate (%) of decrease in ejection velocity when each of the cyan
inks shown in Table 5 was ejected at nonejection intervals of 6 seconds
was determined with respect to an ejection velocity when each of the cyan
inks was ejected at nonejection intervals of 0.3 msec. The intermittent
ejection stability was evaluated on the basis of the rate of decrease.
The ejection velocity of the ink was determined as follows: Regarding ink
droplets ejected from the recording head, ejection was synchronized with
light emission from an electronic flash-type observation system. The
ejection velocity was calculated on the basis of the moving distance of
an ink droplet from 5 μsec to 30 μsec after ejection. Evaluation
criteria are described below. Table 5 shows the results. In aspects of
the present invention, according to the following evaluation criteria,
grade B or higher was defined as an acceptable level, and grade C or
lower was defined as an unacceptable level.

[0079] An ink jet recording apparatus was used which included the image
forming portion illustrated in FIGURE. Specifically, the apparatus
included a recording head configured to eject ink by the application of
thermal energy, and a humidifying unit (second humidifying unit in
FIGURE) configured to supply humidified air into a gap between a
recording head and a recording medium at the time of image formation.
Recording conditions were set as follows: volume per ink droplet: 2.8 pL,
resolution: 2400 dpi×1200 dpi, and the number of arrays of nozzles:
8. An image formed under conditions in which eight ink droplets each
having a volume of 2.8 pL were applied to a 1/600 inch× 1/600 inch
unit region was defined as an image with a recording duty of 100%.

[0080] AA: The rate of decrease in ejection velocity was less than 30%.

[0081] A: The rate of decrease in ejection velocity was 30% or more and
less than 40%.

[0082] B: The rate of decrease in ejection velocity was 40% or more and
less than 50%.

[0083] C: The rate of decrease in ejection velocity was 50% or more.

[0084] Bronzing Resistance of Secondary Color Image

[0085] Blue images were each formed on a recording medium (trade name:
Canon Photo Paper-Gloss Gold GL-101, manufactured by CANON KABUSHIKI
KAISHA) including an ink-receiving layer using cyan and magenta inks
shown in Table 5. The images were secondary color images formed under the
same ratio of the amount of the cyan ink to the amount of the magenta ink
applied, the images having 16 different recording duties between 10% and
160% in steps of 10%. An ink jet recording apparatus and recording
conditions used were the same as those in the foregoing evaluation of the
intermittent ejection stability. An image formed under conditions in
which a total of eight droplets of the cyan and magenta inks, each
droplet having a volume of 2.8 pL, were applied to a 1/600 inch×
1/600 inch unit region was defined as a secondary color image with a
recording duty of 100%.

[0086] With respect to the resulting evaluation samples, the image in
which the bronzing phenomenon occurred was visually identified. The
recording duty of the image was defined as recording duty at which the
bronzing phenomenon occurred. The evaluation of the bronzing resistance
of each secondary color image was made on the basis of the recording
duty. Here, a higher recording duty at which the bronzing phenomenon
occurred indicates the ink having higher bronzing resistance. Evaluation
criteria were described below. Table 5 shows the results. In aspects of
the present invention, according to the following evaluation criteria,
grade B or higher was defined as an acceptable level, and grade C or
lower was defined as an unacceptable level.

[0087] AA: The recording duty at which the bronzing phenomenon occurred
was 160% or more.

[0088] A: The recording duty at which the bronzing phenomenon occurred was
150% or more and less than 160%.

[0089] B: The recording duty at which the bronzing phenomenon occurred was
140% or more and less than 150%.

[0090] C: The recording duty at which the bronzing phenomenon occurred was
less than 140%.

[0091] Ozone Resistance of Secondary Color Image

[0092] Evaluation samples were produced using the cyan and magenta inks
shown in Table 5 in the same way as the foregoing samples for the
evaluation of bronzing resistance. The image density of a portion of an
image with a recording duty of 50% of the evaluation sample was measured
(the resulting image density was defined as "image density d1 before
an ozone resistance test"). This evaluation sample was subjected to ozone
exposure with an ozone testing apparatus (trade name: OMS-H, manufactured
by Suga Test Instruments Co., Ltd.) at an ozone gas concentration of 10
ppm, a relative humidity of 60%, and a temperature in a chamber of
23° C. for 5 hours. Then the image density of the portion of the
image with a recording duty of 50% of the ozone-exposed evaluation sample
was measured (the resulting image density was defined as "image density
d2 after the ozone resistance test"). The image density was measured
with a spectrophotometer (trade name: Spectrolino, manufactured by
Gretag-Macbeth) using a light source (D50) at a view angle of 2°
and was defined as the average optical density of a cyan component and a
magenta component. A residual image density (%) was calculated from the
expression d2/d1×100 using the resulting d1 and
d2 to evaluate the ozone resistance of the secondary color image.
Evaluation criteria were described below. Table 5 shows the results. In
aspects of the present invention, according to the following evaluation
criteria, grade A or higher was defined as an acceptable level, and grade
B or lower was defined as an unacceptable level.

[0093] A: The residual image density was 90% or more.

[0094] B: The residual image density was 80% or more and less than 90%.

[0095] C: The residual image density was less than 80%.

[0096] Suppression of Increase in Concentration of Magenta Ink at
Beginning Portion

[0097] After 100 droplets of each of the magenta inks shown in Table 5
were ejected at nonejection intervals of 0.3 msec, solid images each
having a recording duty of 25% were recorded at nonejection intervals of
6 seconds. An ink jet recording apparatus, recording conditions, and the
definition of the recording duty used were the same as those in the
evaluation of the intermittent ejection stability. A recording medium
used was the same as that in the evaluation of the bronzing resistance.
The resulting evaluation samples were visually checked to evaluate the
suppression of the increase in the concentration of the magenta ink at a
beginning portion. Evaluation criteria were described below. Table 5
shows the results. In aspects of the present invention, according to the
following evaluation criteria, grade B or higher was defined as an
acceptable level, and grade C was defined as an unacceptable level.

[0098] AAA: The concentration at a beginning of the image was not
increased.

[0099] AA: The concentration at a beginning of the image was very slightly
increased.

[0100] A: The concentration at a beginning of the image was slightly
increased.

[0101] B: The concentration at a beginning of the image was increased.

[0102] C: The concentration at a beginning of the image was significantly
increased.

[0103] While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is not
limited to the disclosed exemplary embodiments. The scope of the
following claims is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures and functions.

[0104] This application claims the benefit of Japanese Patent Application
No. 2010-141941 filed Jun. 22, 2010, which is hereby incorporated by
reference herein in its entirety.